Splittable multicomponent fiber with high temperature, corrosion resistant polymer

ABSTRACT

The present invention provides a splittable, multicomponent fiber or filament comprising a first polymer that has a high melting point and does not degrade in a corrosive environment, and a second polymer that has a high melting point but that is degradable in a corrosive environment. The multicomponent fiber or filament is particularly useful in filtration media.

FIELD OF THE INVENTION

The present invention is related to multicomponent fibers. In particular, the invention is related to multicomponent fibers comprising at least one high melting point, corrosion resistant polymer and fabrics made from such fibers and from microfilaments obtainable from such multicomponent fibers.

BACKGROUND

Filtration processes are used to separate specific compounds (often of one phase) from a fluid stream (often of another phase) by passing the fluid stream through filtration media, which traps the specific compounds for separation, such as by entrainment or suspension. For example, the fluid stream may be a liquid stream containing a solid particulate. Likewise, the fluid stream may be a gas stream containing a liquid or solid aerosol. Many properties may be considered in selecting a particular filtration media, including the ability of the media to retain the compounds to be filtered, temperature stability, chemical stability (e.g., corrosion resistance), physical strength of the media to withstand filtering conditions, and cost.

Filtration media commonly include fabrics formed of natural, synthetic, metallic, and glass fibers. For use in corrosive environments, filters are generally formed of fibers having chemical resistance. For example, power plants often employ baghouse filters, which are subject to a stream for filtration characterized by a high temperature, corrosive environment. U.S. Pat. No. 5,586,997, which is incorporated by reference in its entirety, provides further disclosure related to bag filters.

A wide range of fabric constructions can be used in filtration media, such as woven, knit, and nonwoven fabrics, including meltspun webs. Non-limiting examples of webs useful in filtration media include carded fiber webs, air-laid fiber webs, wet-laid fiber webs, meltblown fiber webs, and spunbond fiber webs.

Fine denier fibers in filtration media can provide benefits in the filtration of extremely small particulates. Fine denier fibers may be used to produce fabrics having smaller pore sizes, thus allowing smaller particulates to be filtered from a fluid stream. In addition, fine denier fibers can provide a greater surface area per unit weight of fiber, which can be beneficial in filtration applications.

One method for preparing fabric from fine denier filaments is meltblown technology. Fine denier meltblown webs have been widely used as filter media as the densely packed fibers of such webs are conducive to providing high filter efficiency (i.e., removal of a high percentage of particles of a given size). Meltblown webs, however typically do not have good physical strength, primarily because less orientation is imparted to the polymer during processing and lower molecular weight resins are generally used. Accordingly, in general practice, meltblown filter media are laminated to at least one separate, self-supporting layer, which adds costs and complexity to the manufacturing process.

Continuous filament or spunbond melt extrusion processes can provide higher strength fibers than meltblown fibers; however, it can be difficult to prepare fine denier fibers, particularly fibers of 2 denier or less, using conventional continuous filament or spunbond melt extrusion processes. Therefore, while filter media produced from nonwoven webs of coarser fibers, such as spunbond and staple fiber webs, have been used in filtration applications, such as stove hood filters, they have not been used as filter media for fine particles.

One method for overcoming such difficulties in continuous filament melt extrusion is to split multicomponent continuous filament or staple fiber into fine denier filaments, or microfilaments, in which each fine denier filament has only one polymer component. Multicomponent fibers, also referred to as composite fibers, may be split into fine denier fibers comprised of the respective components if the composite fiber is formed from polymers which are incompatible in some respect. The single composite filament thus becomes a bundle of individual microfilaments. See, for example, U.S. Pat. Nos. 5,783,503 and 5,759,926, which are incorporated herein by reference, and which disclose splittable multicomponent fibers containing polypropylene, such as splittable polyester/polypropylene and nylon/polypropylene fibers.

A number of processes are known for separating the fine denier filaments from multicomponent fibers. The particular process employed depends upon the specific combination of components comprising the fiber, as well as their configuration. One common process by which to divide a multicomponent fiber involves mechanically working the fiber. For example, hydroentangling is commonly employed to effect fiber separation during fabric formation. Other, non-limiting examples of mechanical means for fiber separation include needle punching, beating, and carding. In some cases drawing on godet rolls may be sufficient for fiber separation. When mechanical action is to be used to separate multicomponent fibers, the fiber components are generally selected to bond poorly with each other to facilitate subsequent separation.

As previously noted, filters employing synthetic fibers are often used in extreme conditions, including high temperature and corrosive environments. Synthetic fibers suitable for use in such environments are often costly. Further, as pollution reduction standards become more stringent, the need for more efficient filtration media increases. Accordingly, there is an increased need to find methods of producing small denier synthetic fibers suitable for high efficiency filters used in high temperature, corrosive environments.

SUMMARY OF THE INVENTION

The present invention provides a segmented, multicomponent fiber or filament that is splittable into a plurality of filaments. The fiber is preferentially splittable into a plurality of microfilaments. The multicomponent fiber, and the microfilaments obtainable therefrom, find various applications in the area of textiles and industry, as well as other areas. The invention also provides various materials formed of the multicomponent fibers and microfilaments, including yarns and fabrics, particularly filtration media.

In one aspect, the invention is directed to a splittable, multicomponent fiber. In a particular embodiment, the multicomponent fiber comprises a first fiber component comprising a polymer with a high melting point and that does not degrade in a corrosive environment. The multicomponent fiber further comprises a second fiber component comprising a polymer having a high melting point but that is degradable in a corrosive environment. Preferentially, the polymers used in the first and second fiber components have a melting point of at least about 180° C. In a preferred embodiment, the multicomponent fiber is segmented, each of the fiber components forming a portion of the outer surface of the fiber, thereby forming distinct, unocclusive cross-sectional segments along the length of the fiber. Further, preferably, the first fiber component is dimensioned to form one or more microfilaments upon splitting of the fiber components, and optionally removing the second fiber component.

The multicomponent fiber is capable of splitting, or dissociation, by various methods. In one embodiment, the fiber is capable of being mechanically dissociated. For example, such mechanical dissociation can include methods, such as carding, crimping, drawing, and high pressure water jet impinging. According to another embodiment, the fiber is capable of being chemically dissociated. For example, the fiber can be subjected to a high temperature, corrosive environment that degrades the second fiber component.

The invention also encompasses various articles incorporating the multicomponent fiber. In one embodiment, there is provided a fabric comprising a multicomponent fiber according to the invention. Preferentially, the fabric includes nonwoven fabrics, woven fabrics, and knit fabrics.

According to another embodiment, there is provided filtration media comprising a multicomponent fiber of the invention. The filtration media can take on various embodiments employable in multiple environments. In a particular embodiment, the filtration media comprises a multicomponent fiber of the invention, wherein the fiber is unsplit or has been split into a plurality of microfilaments, either before or after formation of the filtration media. In one preferred embodiment, the filtration media further comprises one or more non-splittable fibers. Preferentially, the non-splittable fiber comprises a polymer that has a high melting point and does not degrade in a corrosive environment.

In another aspect, the invention is directed to a method for preparing a microfilament filter. The method is particularly characterized in that the microfilament filter is capable of preparation at a point of use. In one embodiment, the method of preparing a microfilament filter comprises providing a filtration media comprising a splittable, multicomponent fiber; installing the filtration media at a point of use; and flowing a stream for filtration through the filtration media. Preferably, the multicomponent fiber used in the filtration media comprises a first fiber component comprising a polymer that has a melting point of at least about 200° C. and that does not degrade in a corrosive environment, and further comprises a second fiber component comprising a polymer that has a melting point of at least about 200° C. and that is degradable in a corrosive environment.

The microfilament filter is capable of preparation at the point of use in that, under high temperature, corrosive conditions, the second fiber component degrades and the first fiber component remains intact as microfilaments. In a particularly preferred embodiment, the microfilaments have a fineness of less than or equal to about 1 denier per filament. In another preferred embodiment, the filtration media further comprises one or more non-splittable fibers comprising a polymer that has a melting point of at least about 200° C. and that does not degrade in a corrosive environment.

The microfilament filter prepared according to the above method is particularly beneficial in that it provides a high efficiency filter capable of use in a high temperature, corrosive environment. Filter performance for a high efficiency filter can be measured as the percentage of particles having a diameter of 1 micron or greater that are retained by the filter. Preferably, the microfilament filter prepared according to the method has a filtration performance of greater than or equal to about 95%.

In yet another embodiment, the invention provides a microfilament filter. Preferably, the microfilament filter is a high efficiency filter adapted for use in a high temperature, corrosive environment, such as in a baghouse filter for use in a power plant.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to assist the understanding of embodiments of the invention, reference will now be made to the appended drawings, which are not necessarily drawn to scale. The drawings are exemplary only, and should not be construed as limiting the invention in any way.

FIGS. 1A-1F provide cross-sectional views of exemplary embodiments of multicomponent fibers according to the present invention;

FIGS. 2A-2B provide cross-sectional and longitudinal views, respectively, of an exemplary fiber according to one embodiment of the invention, wherein the fiber has been mechanically dissociated;

FIG. 3 provides a flow diagram illustrating a fabric formation process according to one embodiment of the invention; and

FIG. 4 schematically illustrates one fabric formation process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described more fully hereinafter in connection with illustrative embodiments of the invention which are given so that the present disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. However, it is to be understood that this invention may be embodied in many different forms and should not be construed as being limited to the specific embodiments described and illustrated herein. Although specific terms are used in the following description, these terms are merely for purposes of illustration and are not intended to define or limit the scope of the invention. Like numbers refer to like elements throughout. As used in this specification and the claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

The present invention is directed to a segmented, splittable, multicomponent fiber or filament comprising two or more fiber components. In general, multicomponent fibers are formed of two or more fiber components (preferentially, polymeric materials) which have been extruded together to provide continuous, contiguous polymer segments extending down the length of the multicomponent fiber. In a particular embodiment, the multicomponent fiber of the invention comprises a first fiber component and a second fiber component. While the invention may be described herein in terms of the first and second fiber components, it is understood that the multicomponent fiber is not limited to two fiber components. Rather, the invention encompasses fibers comprising two or more fiber components. Furthermore, while the invention may be described herein in relation to a “fiber”, it is understood that the term encompasses fibers of finite length, such as conventional staple fiber, as well as substantially continuous structures, such as filaments. In one embodiment, the multicomponent fiber of the invention comprises a fiber selected from the group consisting of continuous filaments, staple fibers, spunbond fibers, and meltblown fibers.

The multicomponent fiber of the invention can take on a number of structural configurations, and any configurations allowing for free dissociation of the individual fiber components are acceptable according to the present invention. Generally, the fiber components are arranged so as to form distinct, unocclusive cross-sectional segments along the length of the fiber so that the first fiber component is not impeded from being separated from the second fiber component (or further fiber components, as desired). In one particularly advantageous embodiment, the multicomponent fiber of the invention takes on a pie-wedge arrangement, such as that illustrated in FIG. 1A. The pie-wedge fiber arrangement illustrated in FIG. 1A is a bicomponent filament 4 having eight alternating segments of triangular shaped wedges comprising the overall “pie”. The wedges comprise a first fiber component 6 and a second fiber component 8. While the pie-wedge filament illustrated in FIG. 1A is a non-hollow fiber, the invention also encompasses embodiments wherein the pie-wedge filament is hollow. Further, while the pie-wedge fiber of FIG. 1A comprises eight wedge segments, it should be recognized that filaments according to the invention can comprise more or less than eight segments.

In addition to the pie-wedge configuration illustrated in FIG. 1A, the multicomponent fiber of the invention can also take on other segmented, splittable fiber configurations. For example, the multicomponent fiber of the invention could take on the configuration illustrated in FIG. 1B, which shows a round fiber 4 segmented into four alternating sections, comprising a first fiber component 6 and a second fiber component 8. Description of further multicomponent fiber construction that may be useful according to the present invention can be found in U.S. Pat. No. 5,108,820; U.S. Pat. No. 5,336,553; and U.S. Pat. No. 5,382,400; which are all incorporated herein by reference.

The multicomponent fibers of the present invention are further advantageous in that they are not limited to configuration as conventional round fibers. Rather, the multicomponent fibers can take on other useful shapes. For example, the inventive multicomponent fiber can take on a segmented rectangular (or ribbon) configuration, as illustrated in FIG. 1C, a segmented oval configuration, as illustrated in FIG. 1D, a multilobal configuration, as illustrated in FIG. 1E, and a segmented cross configuration, as illustrated in FIG. 1F. Further description of multicomponent fibers of unconventional shape that may be useful according to the present invention can be found in U.S. Pat. No. 5,277,976; U.S. Pat. No. 5,057,368; and U.S. Pat. No. 5,069,970; which are all incorporated herein by reference.

Both the shape of the fiber and the configuration of the components therein can depend upon various factors including, but not necessarily limited to, the equipment used in the preparation of the multicomponent fiber, the process conditions, and the melt viscosities of the various fiber components. Accordingly, a wide variety of fiber configurations are possible.

As can be seen in FIGS. 1A-F, the multicomponent fiber of the invention is typically formed to have a configuration such that one component does not fully surround, or encapsulate, the other components. One example of a configuration where one fiber component completely surrounds the other fiber components is an islands-in-the-sea configuration. While such embodiments are not specifically excluded by the present invention, it is generally preferred that the multicomponent fiber of the invention take on a configuration wherein each fiber component forms a portion of the outer surface of the fiber.

In conventional multicomponent fibers, so as to provide dissociable properties to the composite fiber, the fiber components are generally chosen so as to be mutually incompatible. In particular, the polymers used for the fiber components do not substantially mix together and are not chemically reactive one with the other. Specifically, when spun together to form a composite fiber, the polymer components exhibit a distinct phase boundary between them so that substantially no blend polymers are formed that may prevent dissociation. Additionally, a balance of adhesion/incompatibility between the components of the composite fiber is considered highly beneficial. The components advantageously adhere sufficiently to each other to allow the unsplit multicomponent fiber to be subjected to conventional textile processing, such as winding, twisting, weaving, or knitting without any appreciable separation of the components until desired. Conversely, it is generally desirable that the polymers be sufficiently incompatible so that adhesion between the components is relatively weak, thereby allowing ready separation at the desired time.

The multicomponent fibers of the present invention can also be subject to the above considerations in that the present multicomponent fibers may be mechanically dissociated, which is described in greater detail below. The multicomponent fiber of the present invention is further characterized, however, in that the fiber is also subject to chemical dissociation, the mechanism of which is made evident according to the following description of the inventive fiber.

In one embodiment of the invention, the multicomponent fiber comprises a first fiber component and a second fiber component. Both fiber components are preferably polymers, however, the fiber components are clearly distinguishable according to the physical properties of the polymers. In particular, the first fiber component comprises a polymer that has a high melting point and that does not degrade in a corrosive environment, and the second fiber component comprises a polymer that also has a high melting point, but that is degradable in a corrosive environment.

The phrase “high melting point” as used herein is intended to refer to melting points above a specified range, particularly melting points above the operating temperatures to which synthetic fibers are exposed in harsh industrial environments, such as in the case of fibers in baghouse filters used in power plants, particularly coal-fired power plants. Accordingly, as applied to the present invention, the phrase “high melting point” is intended to refer to melting point temperatures of about 160° C. or greater, preferably about 170° C. or greater, more preferably about 180° C. or greater, still more preferably about 190° C. or greater, and most preferably about 200° C. or greater. In one embodiment, “high melting point” refers to a melting point temperature in the range of about 160° C. to about 300° C., preferably about 180° C. to about 280° C., more preferably about 200° C. to about 250° C.

As previously noted, the first fiber component of the inventive fiber is distinguishable from the other fiber components in that the first fiber component does not degrade in a corrosive environment. The phrase “corrosive environment” is generally understood to refer to an atmosphere having conditions present for facilitating a physical breakdown of an item through chemical interactions of the environment with the item. A corrosive environment may be correlated to the presence of various chemical agents, including alkalies, acids, oxidizing agents, and organic solvents. For example, in the baghouse of a coal-fired power plant, sulfuric acid is formed when sulfur released from the coal reacts with moisture, such as condensation on the baghouse filter. Accordingly, a corrosive environment could refer to an environment where sulfuric acid is present.

The polymer comprising the first fiber component does not degrade in a corrosive environment. Accordingly, the polymer used in the first fiber component would be expected to resist degradation in the presence of corrosive agents. In particular, the polymer used in the first fiber component does not degrade in the presence of strong bases, mineral acids, organic acids, oxidizing agents, or organic solvents. Conversely, the polymer comprising the second fiber component does degrade in a corrosive environment. Accordingly, the polymer used in the second fiber component would be expected to be degradable in the presence of corrosive agents. In particular, the polymer used in the second fiber component is degradable in the presence of strong bases, mineral acids, organic acids, oxidizing agents, or organic solvents. In one particular embodiment, the polymer used in the second fiber component is degradable in the presence of acids, and specifically acids formed as by-products of the combustion of coal, such as sulfuric acid.

In one particular embodiment of the invention, the first fiber component comprises a polymer that has a melting point of at least about 200° C. Preferably, the first fiber component comprises a polymer that has a melting point of at least about 225° C., more preferably at least about 250° C., still more preferably at least about 275° C., even more preferably at least about 285° C., and most preferably at least about 300° C.

As would be recognizable to the skilled artisan, many different polymers could be used in the first fiber component according to the invention. Any polymer exhibiting the physical properties described herein with respect to melting point and degradation resistance in a corrosive environment could be used as the first polymer component in the multicomponent fiber of the invention. In one embodiment, the first fiber component comprises a polymer selected from the group consisting of polyphenylene sulfide, fluoropolymers (e.g., polytetrafluoroethylene), chlorofluoropolymers, (e.g., HALAR®, which is an ethylene/chlorotrifluoroethylene copolymer), epoxies, silicones, polymethylpentene, mixtures thereof, copolymers thereof, and terpolymers thereof.

In another particular embodiment of the invention, the multicomponent fiber further comprises a second fiber component also comprising a polymer that has a melting point of at least about 200° C. Preferably, the second fiber component comprises a polymer that has a melting point of at least about 225° C., more preferably at least about 250° C., still more preferably at least about 275° C., even more preferably at least about 285° C., and most preferably at least about 300° C. While the polymers used in the first and second fiber components exhibit similar melt characteristics, the polymer used in the second fiber component is different from the polymer used in the first fiber component.

As would again be recognizable to the skilled artisan, many different polymers could be used in the second fiber component according to the invention. In particular, any polymer exhibiting the physical properties described herein with respect to melting point and degradation in a corrosive environment could be used as the second polymer component in the multicomponent fiber of the invention. In one embodiment, the second fiber component comprises a polymer selected from the group of polyesters and polyamides. Preferably, the second fiber component comprises a polymer selected from the group consisting of polycyclohexylene dimethyl terephthalate (PCT), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), poly(trimethylene) terephthalate (PTT), polyethylene naphthalate (PEN), nylon 6, and nylon 6,6.

Preferentially, the first fiber component and the second fiber component of the inventive multicomponent fiber are present in defined ratios based on the overall weight of the multicomponent fiber. In one embodiment, the first fiber component comprises at least about 50% by weight of the multicomponent fiber. Preferably, the first fiber component comprises at least about 60% by weight of the multicomponent fiber, more preferably at least about 70% by weight, and most preferably at least about 75% by weight of the multicomponent fiber.

Each of the fiber components can optionally include additional ingredients. Examples of materials that could be used as additional components include, but are not limited to, antioxidants, stabilizers, surfactants, waxes, flow promoters, solid solvents, particulates, and other materials added to enhance processability of the first fiber component or the second fiber component of the inventive multicomponent fiber. In particular, it may be useful to use pigments with one or both of the first and second fiber components. The same pigment may be employed in both fiber components, or, in an alternative embodiment, the components may each contain pigments of differing colors. Further, the invention encompasses the addition of other additives that may be useful for providing beneficial properties to the finished product, such as antimicrobials, flame retardants, UV absorbers, and the like. These and other additives can be used in conventional amounts.

As previously noted, the multicomponent fiber of the present invention can be provided as staple fibers of varying finite lengths, continuous filaments, spunbond fibers, and meltblown fibers. The fibers can also be described in terms of fiber fineness on a denier scale, which is a commonly used expression of fiber diameter, and which is defined as the weight in grams of 9000 meters of the fiber. As understood in the art, a lower denier value indicates a finer fiber, while a higher denier value indicates a thicker, or heavier, fiber. The fineness of the multicomponent fibers prepared according to the present invention can vary depending upon the fiber formation. Generally, the multicomponent fibers of the invention can have a fineness of about 1 denier per filament (dpf) to about 60 dpf, more preferably about 1.5 dpf to about 20 dpf, most preferably about 2 dpf to about 10 dpf.

The multicomponent fiber of the present invention is characterized, in one aspect, in that the overall fiber is splittable, through mechanical dissociation or chemical dissociation, to provide a plurality or fine denier filaments, or microfilaments, each formed of the individual fiber components that make up the overall multicomponent fiber. In particular, the first fiber component of the multicomponent fiber is dimensioned so as to form a microfilament upon dissociation from the second fiber component (which is understood to mean the same as the second fiber component being dissociated from the first fiber component). As used herein, the terms “fine denier filaments” and “microfilaments” are interchangeable and are intended to include sub-denier filaments and ultra-fine filaments. Sub-denier filaments typically have denier values in the range of 1 dpf or less. Ultra-fine filaments typically have denier values in the range of about 0.1 dpf to about 0.3 dpf. It is also understood according to the invention that the term microfilaments relates to continuous filaments, as well as staple fibers. In one embodiment, the microfilaments formed by dissociation of the multicomponent fiber exhibit have a fineness in the range of about 0.05 dpf to about 1.0 dpf, preferably about 0.1 dpf to about 0.7 dpf, more preferably about 0.1 dpf to about 0.5 dpf.

FIG. 2 illustrates one embodiment of a multicomponent fiber of the invention that has been separated into a fiber bundle 10 of microfilaments. As seen in FIG. 2, the multicomponent fiber has been split into four microfilaments 6 comprising the first fiber component and four microfilaments 8 comprising the second fiber component, thereby providing an eight filament fiber bundle 10. In one embodiment of the invention, the multicomponent fiber is splittable, either mechanically or chemically, into 4 to 48 microfilaments. Preferably, the multicomponent fiber is splittable into 6 to 36 microfilaments, more preferably 8 to 20 microfilaments. In one embodiment, the multicomponent fiber is splittable into 16 to 32 microfilaments.

As the multicomponent fibers of the invention, and the microfilaments produced therefrom, are subject to mechanical and/or chemical stresses to facilitate splitting, it is preferable for the fibers, and microfilaments, to have a suitable tenacity. As is understood in the art, tenacity describes the tensile strength of a fiber (i.e., the force at which the fiber ruptures or breaks) and is generally provided in terms of grams per denier (gpd), or the force in grams required to break a given filament or fiber bundle divided by that filament or fiber bundle's denier value. In one embodiment, the multicomponent fibers and microfilaments of the invention exhibit a tenacity of about 1.0 gpd to about 5 gpd, preferably about 1.5 gpd to about 4.5 gpd, more preferably about 2 gpd to about 4 gpd.

As noted above, the multicomponent fiber of the invention, in one embodiment, is capable of being mechanically dissociated into the separate fiber component microfilaments. In particular, the first fiber component is dimensioned to form a microfilament upon dissociation. Mechanical dissociation can be by any means that provides sufficient flex or mechanical action to the multicomponent fiber to fracture and separate the individual fiber components of the composite fiber. As used herein, the terms “splitting,” dissociating,” or “dividing” are intended to mean that at least one of the fiber components is separated completely or partially from the original multicomponent fiber. Partial splitting can mean dissociation of some individual segments from the fiber, or dissociation of pairs or groups of segments (which remain together in these pairs or groups) from other individual segments, or pairs or groups of segments from the original fiber. As seen in FIG. 2, the resultant microfilaments can remain in proximity to the remaining components, thereby providing a coherent fiber bundle 10 of microfilaments 6 and 8, originating from a common multicomponent fiber. However, as the skilled artisan will appreciate, in some processing techniques, such as hydroentanglement, or where the fibers are split prior to fabric formation, the microfilaments originating from a common fiber source may be further removed from one another.

According to another embodiment of the invention, there is provided a fabric comprising a multicomponent fiber, as described herein. A fabric according to the invention can be prepared through any method recognizable in the art as useful for preparing fabrics using synthetic fibers. In particular, the fabric according to the invention comprises nonwoven fabrics, woven fabrics, and knit fabrics.

One process for making a fabric in accordance with one embodiment of the invention is illustrated diagrammatically in FIG. 3. Specifically, FIG. 3 illustrates an extrusion process 14, followed by a draw process 16, a staple process 18, a carding process 20, and a fabric formation process 22.

Extrusion processes for making multicomponent continuous filament fibers are known and need not be described here in detail. Generally, to form a multicomponent fiber, at least two polymers are extruded separately and fed into a polymer distribution system wherein the polymers are introduced into a spinneret plate. The polymers follow separate paths to the fiber spinneret and are combined in a spinneret hole. The spinneret is configured so that the extrudant has the desired overall fiber cross section (e.g., round, trilobal, etc.). Such a process is described, for example, in U.S. Pat. No. 5,162,074, which is incorporated herein by reference in its entirety.

In the present invention, a first polymer that has a high melting point and that does not degrade in a corrosive environment, such as polyphenylene sulfide, and a second polymer that has a high melting point and that is degradable in a corrosive environment, such as polyethylene terephthalate, are fed into the polymer distribution system. The polymers typically are selected to have melting points such that the polymers can be spun as a polymer throughput that enables the spinning of the components through a common capillary at substantially the same temperature without degrading one of the components.

Following extrusion through the die, the resulting thin fluid strands, or filaments, remain in the molten state for some distance before they are solidified by cooling in a surrounding fluid medium, which may be chilled air blown through the strands. Once solidified, the filaments are taken up on a godet or other take-up surface. In a continuous filament process, the strands are taken up on a godet, which draws down the thin fluid streams in proportion to the speed of the take-up godet. Continuous filament fiber may further be processed into staple fiber. In processing staple fibers, large numbers (e.g., 10,000 to 1,000,000 strands) of continuous filament are gathered together following extrusion to form a tow for use in further processing.

Rather than being taken up on a godet, continuous multicomponent fiber may also be melt spun as a direct laid, nonwoven web via a jet process. For example, in a spunbonding process, the strands are collected in a jet following extrusion through the die, such as for example, an air attenuator, and then blown onto a take-up surface, such as a roller or a moving belt, to form a spunbond web. Alternatively, direct laid composite fiber webs may be prepared by a meltblown process, in which air is ejected at the surface of a spinneret to simultaneously draw down and cool the thin fluid polymer streams, which are subsequently deposited on a take-up surface in the path of cooling air to form a fiber web.

Regardless of the type of melt spinning procedure which is used, the thin fluid streams are typically melt drawn in a molten state (i.e., before solidification occurs) to orient the polymer molecules for good tenacity. Typical melt draw down ratios known in the art may be utilized. The skilled artisan will appreciate that specific melt draw down is not required for meltblowing processes.

When a continuous filament or staple process is employed, it may be desirable to subject the strands to a draw process. In the draw process, the strands are typically heated past their glass transition point and stretched to several times their original length using conventional drawing equipment, such as, for example, sequential godet rolls operating at differential speeds. Typical draw ratios can depend upon polymer type. For example, draw ratios of about 2 to about 5 times are typical for polyolefin fibers. Optionally, the drawn strands may be heat set to reduce any latent shrinkage imparted to the fiber during processing.

If staple fiber is being prepared, following drawing in the solid state, the continuous filaments are cut into a desirable fiber length. The length of the staple fibers generally ranges from about 25 to about 50 millimeters, although the fibers can be longer or shorter as desired. See, for example, U.S. Pat. No. 4,789,592 and U.S. Pat. No. 5,336,552, which are incorporated herein by reference. Optionally, the fibers may be subjected to a crimping process prior to the formation of staple. Crimped composite fibers are highly useful for producing lofty woven and nonwoven fabrics since the microfilaments split from the multicomponent fibers largely retain the crimps of the composite fibers, and the crimps increase the bulk, or loft, of the fabric. Such lofty fine fiber fabric of the present invention exhibits cloth-like textural properties (e.g., softness, drapability, and hand) as well as the desirable strength properties of a fabric containing highly oriented fibers.

The staple fiber thus formed is then fed into a carding process. A more detailed schematic illustration of a carding process is provided in FIG. 4. As shown therein, the carding process can include the step of passing spun yarns 26 comprising staple fibers through a carding machine 28 to align the fibers of the yarn as desired, typically to lay the fibers in roughly parallel rows, although the staple fibers may be oriented differently. The carding machine 28 is comprised of a series of revolving cylinders 34 with surfaces covered in teeth. These teeth pass through the yarn as it is conveyed through the carding machine on a moving surface, such as a drum 30. The carding process produces a fiber web 32.

The carded fiber web 32 can be subjected to a fabric formation process to impart cohesion to the fiber web. In one embodiment, the fabric formation process includes the step of bonding the fibers of fiber web 32 together to form a coherent unitary nonwoven fabric. The bonding step can be any known in the art, such as mechanical bonding, thermal bonding, and chemical bonding. Typical methods of mechanical bonding include hydroentanglement and needle punching.

FIG. 4 further illustrates a schematic of one hydroentangling process suitable for use in the present invention. As shown in FIG. 4, the fiber web 32 is conveyed longitudinally to a hydroentangling station 40 wherein a plurality of manifolds 42, each including one or more rows of fine orifices, direct high pressure water jets through fiber web 32 to intimately hydroentangle the staple fibers, thereby providing a cohesive, nonwoven fabric 52.

The hydroentangling station 40 is constructed in a conventional manner as known to the skilled artisan and as described, for example, in U.S. Pat. No. 3,485,706, which is hereby incorporated by reference. As known to the skilled artisan, fiber hydroentanglement is accomplished by jetting liquid, typically water, supplied at a pressure of from about 200 psig up to 4000 psig or greater to form fine, essentially columnar, liquid streams. The high pressure liquid streams are directed toward at least one surface of the composite web. In one embodiment of the invention water at ambient temperature and 200 bar is directed towards both surfaces of the web. The composite web is supported on a foraminous support screen 44 which can have a pattern to form a nonwoven structure with a pattern or with apertures or the screen can be designed and arranged to form a hydraulically entangled composite which is not patterned or apertured. The fiber web 32 can be passed through the hydraulic entangling station 40 a number of times for hydraulic entanglement on one or both sides of the composite web or to provide any desired degree of hydroentanglement.

Optionally, the nonwoven webs and fabrics of the present invention may be thermally bonded. In thermal bonding, heat and/or pressure are applied to the fiber web or nonwoven fabric to increase its strength. Two common methods of thermal bonding are air heating, used to produce low-density fabrics, and calendering, which produces strong, low-loft fabrics. Hot melt adhesive fibers may optionally be included in the web of the present invention to provide further cohesion to the web at lower thermal bonding temperatures.

As an alternative to producing a dry-laid nonwoven fabric, such as previously described, a nonwoven fabric may be formed in accordance with the instant invention by direct-laid means. In one embodiment of direct laid fabric, continuous filament is spun directly into nonwoven webs by a spunbonding process. In an alternative embodiment of direct laid fabric, multicomponent fibers of the invention are incorporated into a meltblown fabric. The techniques of spunbonding and meltblowing are known in the art and are discussed in various patents, e.g., U.S. Pat. No. 3,987,185; U.S. Pat. No. 3,972,759; and U.S. Pat. No. 4,622,259; which are incorporated herein by reference. The fiber of the present invention may also be formed into a wet-laid nonwoven fabric, via any suitable technique known in that art.

While particularly useful in the production of nonwoven fabrics, the fibers of the invention can also be used to make other textile structures such as but not limited to woven and knit fabrics. Yarns prepared for use in forming such woven and knit fabrics are similarly included within the scope of the present invention. Such yarns may be prepared from the continuous filament or spun yarns comprising staple fibers of the present invention by methods known in the art, such as twisting or air entanglement.

In one embodiment of the invention, the fabric formation process itself is used to mechanically dissociate the multicomponent fiber of the invention into microfilaments comprising the individual fiber components. Stated differently, forces applied to the multicomponent fibers of the invention during fabric formation in effect split or dissociate the polymer components to form microfilaments. The resultant fabric thus formed is comprised, for example, of a plurality of microfilaments 6 and 8, such as shown in FIG. 2, and described previously. Mechanical dissociation can take place during one or more aspects of the fabric forming process. In a particular, complete or partial mechanical dissociation can be achieved through carding, crimping, drawing, and high pressure water jet impinging, such as the hydroentangling process. Optionally, the composite fiber may be divided after the fabric has been formed by application of mechanical forces thereto. In addition, the multicomponent fiber of the present invention may be separated into microfilaments before or after formation into a yarn. Still further, the multicomponent fiber may be separated into the individual fiber component microfilaments prior to implementation of any of the above-described fabric formation process steps, or other fabric formation process steps as may be known in the art.

As noted above, the multicomponent fiber of the invention, in another embodiment, is capable of being chemically dissociated. The multicomponent fiber generally comprises a first fiber component comprising a polymer that has a high melting point and that does not degrade in a corrosive environment. The multicomponent fiber further comprises a second fiber component comprising a polymer that also has a high melting point but that is degradable in a corrosive environment. Accordingly, the multicomponent fiber is capable of being chemically dissociated by introducing the fiber to a corrosive environment. For example, in one embodiment, the second fiber component can comprise a polymer that is degradable in an acidic environment. By introducing the multicomponent fiber to an acidic environment, the second fiber component, being degradable in such an environment, degrades. The first fiber component, not being degradable in such an environment, remains intact. Therefore, the multicomponent fiber is chemically dissociated by chemically degrading the second fiber component to free the first fiber component, which preferably is dimensioned to form microfilaments.

The multicomponent fibers, the microfilaments prepared therefrom, and the fabrics prepared from the multicomponent fibers and the microfilaments, as described above, are particularly beneficial in that a variety of useful products can be prepared using the fibers, microfilaments, and fabrics of the invention. In particular, the various products prepared according to the invention are further useful in the preparation of filtration media.

Many types of filtration media are known in the art and find a variety of uses in industry, as well as in public and private structures, such as homes and commercial buildings. Non-limiting examples of industrial uses for filtration media include bag filters, air filters, mist eliminators, and the like. Bag filters are known for use in filtering paints and coatings, especially hydrocarbon-based paints and primers, chemicals, petrochemical products, and the like. Air filters are useful in filtering large or small volumes of air. Small air volume applications include face mask filters. Large volumes of air are advantageously filtered using electret filters. Electret air filters are particularly useful in applications such as furnace filters, automotive cabin filters, and room air cleaner filters. Mist eliminators, used to remove liquid or solid airborne particles, are employed in a wide range of industrial applications generating waste gas streams. Filtration media prepared according to the present invention would find use in all of the above, as well as other areas that would be recognizable to the skilled artisan.

Generally speaking, filtration media are useful for removing an undesirable component of a moving stream, which is usually a gas or a liquid. Fabric filter media are particularly useful for removing particulate matter from a gas stream. Performance of fabric filter media is strongly dependant upon the type of fabric used. In the case of nonwoven fabrics, particularly, performance can be dictated by the characteristics of the individual fibers or microfilaments used in the preparation thereof. A fabric for use as filtration media must be able to efficiently collect the matter desired for removal from a stream, must be compatible with the stream flowing through the filter media, and is preferably easily amenable to cleaning and re-use.

Filtration media according to the present invention can be prepared using the multicomponent fiber, microfilaments obtainable from the multicomponent fiber, or fabric incorporating the multicomponent fiber or microfilaments of the invention. Preferably, when the multicomponent fiber is used in preparing filtration media, the fiber is either mechanically or chemically dissociated to form microfilaments, said dissociation occurring either before or after formation of the filtration media. In one particular embodiment, the invention provides a filtration media comprising a multicomponent fiber comprising a first fiber component comprising a polymer that has a melting point of at least about 200° C. and that does not degrade in a corrosive environment, the first fiber component being dimensioned to form a microfilament, and a second fiber component comprising a polymer that has a melting point of at least about 200° C. and that is degradable in a corrosive environment, wherein each of the fiber components forms a portion of the outer surface of the fiber and form distinct, unocclusive cross-sectional segments along the length of the fiber. In yet a further embodiment, the invention provides a filter media as described above, wherein the filtration media further comprises one or more non-splittable fiber. Preferably, the non-splittable fiber has a melting point of at least about 200° C. and does not degrade in a corrosive environment. Non-limiting examples of non-splittable fibers useful for incorporation into the filtration media of the invention include polyimides, aromatic polyamides (aramids), such as NOMEX®, glass fibers, and imidazoles, such as polybenzimidazole (PBI).

The microfilaments of the invention are particularly useful in preparing filtration media as they provide the tensile properties, insensitivity to moisture, and high surface area considered beneficial in filtration media. In addition, articles, such as filter media, prepared according to the invention and comprising microfilaments of the first fiber component, as described herein, possess superior chemical resistance and are advantageously used in corrosive environments.

Accordingly, in one embodiment of the invention, there is provided a microfilament filter comprising a polymer that has a high melting point and that does not degrade in a corrosive environment. Preferably, the microfilaments in the filter have a fineness of less than or equal to about 1 dpf. In one preferred embodiment, the polymer used in the microfilaments comprises polyphenylene sulfide.

Filtration media prepared according to the present invention is further characterized in that it provides high efficiency filtration performance. Filtration performance can generally be described, or rated, in terms of the percentage of particles of a defined size that are retained by the filter when a stream carrying the particles passes through the filter. Accordingly, filter performance is understood to be improved by retaining a higher percentage of particles of smaller size.

Filtration media including microfilaments, as described, are particularly efficient and exhibit a high performance rating. Accordingly, in one embodiment, the microfilament filter of the invention has a filtration performance such that greater than or equal to about 95% of particles having a diameter of 1 micron or greater are retained by the filter. Preferably, greater than or equal to about 99% of particles having a diameter of 1 micron or greater are retained by the filter. In one particularly preferred embodiment, greater than or equal to about 99.9% of particles having a diameter of 1 micron or greater are retained by the filter.

Such high efficiency filters are particularly beneficial in that they meet standards set by the United States Environmental Protection Agency (EPA) under the PM2.5 designation. According to EPA National Ambient Air Quality Standards (NAAQS), particulate matter having a size of 2.5 microns or less are designated PM2.5, and emissions of such particulates are monitored to ensure levels remain below set standards. The filtration media of the present, arising the unique microfiber construction, is further beneficial in that it prevents small particulates from penetrating deeply into the filtration media. Accordingly, the filtration media allows for easier cleaning and removal of trapped particulate matter.

One particular application where filtration media according to the present invention finds use is the field of baghouse filters. Baghouse filters are well understood in the art and therefore do not require detailed discussion herein. A baghouse filter generally comprises one or a series of fabric bags, or flat supported envelopes, contained within a housing, which has a stream inlet, a stream outlet, a collection hopper, and typically a cleaning mechanism for periodic removal of filtrate from the filter. In operation, a stream (such as a gas) containing particulate matter flows through the bag filters, which remove the particulate matter from the stream. In industrial use, baghouse filters are capable of filtering in excess of one million cubic feet of air per minute.

As baghouse filters generally find use in industrial settings, the stream for filtration often presents an inhospitable environment. As previously noted, baghouse filters are often used in power plants, particularly those wherein power production include combustion of a carbon-containing fuel, such as coal-fired and oil-fired power plants. For example, in coal-fired or oil-fired power plants, a baghouse filter system may be positioned to receive exhaust directly from a stoker boiler. Primary problems encountered with such applications include the presence of sulfur in the fuel (e.g., coal or oil), which leads to the formation of acids from sulfur dioxide (SO₂) and sulfur trioxide (SO₃) in the exhaust. Further, alkaline additives (such as dolomite and limestone) may be injected upstream of baghouse inlets to reduce the SO₂ and SO₃ present in the exhaust. Such exhaust may also include nitrates (NO₃) and nitrites (NO₂), as well as significant amounts of hydrochloric acid (HCl). Accordingly, fabric filter media used in baghouse filters encounter high temperatures, as well as corrosive conditions, such as high acidity or alkalinity.

The multicomponent fiber of the present invention, as well as fabric made therefrom, is particularly useful in such environments. As noted above, the multicomponent fiber of the invention comprises a first fiber component comprising a polymer that has a high melting point and that does not degrade in a corrosive environment, such as the acidic or alkaline conditions encountered in a baghouse filter. Therefore, in one embodiment, the invention provides filtration media comprising the multicomponent fiber as described herein. In another embodiment, the invention provides a fabric comprising the multicomponent fiber, wherein the fabric is particularly useful as filtration media. In yet another embodiment, the invention provides a microfilament filter comprising a microfilament obtained through dissociation of the multicomponent fiber of the invention.

In light of the novel composition of the multicomponent fiber, as described herein the invention is further characterized in that, in one particular aspect, there is provided a method for preparing a microfilament filter at a point of use. Preferably, the point of use wherein the microfilament filter is prepared exhibits high temperature, corrosive conditions. In one particular embodiment, the point of use is a baghouse filter.

In a preferred embodiment according to this aspect of the invention, there is provided a method of preparing a microfilament filter, wherein the method comprises providing a filtration media comprising a splittable, multicomponent fiber as described herein comprising a first fiber component and a second fiber component, installing the filtration media at the desired point of use, and flowing a stream for filtration through the filtration media under conditions such that the second fiber component degrades and the first fiber component remains intact as microfilaments. Preferentially, the microfilaments have a fineness of less than or equal to about 1 dpf.

In a particularly preferred embodiment, the first fiber component of the multicomponent fiber comprises a polymer that has a melting point of at least about 200° C. and that does not degrade in a corrosive environment; and the second fiber component comprises a polymer that has a melting point of at least about 200° C. and that is degradable in a corrosive environment. Preferentially, each of the fiber components forms a portion of the outer surface of the multicomponent fiber and form distinct, unocclusive cross-sectional segments along the length of the fiber.

In yet a further embodiment, the method incorporates the use of a filter media as described above, wherein the filtration media further comprises one or more non-splittable fiber. Preferably, the non-splittable fiber has a melting point of at least about 200° C. and does not degrade in a corrosive environment.

The method described above allows for in situ preparation of a microfilament filter through use of a filter media comprised of a multicomponent fiber due to the unique composition of the multicomponent fiber of the invention. Preparation of microfilaments, particularly microfilaments comprising polymers useful in high temperature, corrosive environments, can be costly and difficult. Further, direct preparation of filtration media from microfilaments can also be difficult and costly. The method of the invention overcomes these obstacles. According to the method, it is possible to prepare a multicomponent fiber wherein one of the fiber components will degrade at the conditions of the desired application and the remaining components will remain intact at the application conditions. The multicomponent fiber is used to prepare a filtration media appropriate for the point of use (i.e., the application site), and the filtration media is installed. A stream for filtration is then passed through the filtration media under application conditions (e.g., high temperature, corrosive conditions). As the second fiber component is designed to degrade at the application conditions, the second fiber component degrades, leaving behind the first fiber component, which is preferentially dimensioned to form a microfilament. Accordingly, the multicomponent fiber is chemically dissociated, thereby forming a microfilament filter at the point of use.

The novel composition of the multicomponent fiber of the invention makes it particularly beneficial in the inventive method. Preparation of the filter media as a larger fiber, instead of the microfilament, simplifies preparation of the filtration media. Further, the degraded second fiber component is easily removed after degradation occurs at the application conditions. For instance, in one embodiment, the degraded second fiber component is entrained within filtered stream exiting the filtration media and is thereby carried away from the filtration media by the stream exiting the filter. In another embodiment, the degraded second fiber component remains entrapped in the formed microfilament filter as part of the filtered matter that is easily removed in a later cleaning step. The later cleaning step can include any cleaning method generally used in the art, such as mechanical shaking, reverse flow (with or without heating), and pulse-jet methods.

The method of the invention also lends itself to customization of the pore size of the resultant microfilament filter, thereby controlling the efficiency of the filter. Such customization can occur through varying the ratio of the first fiber component to the second fiber component in the multicomponent fiber. Such ratio is generally within the ranges previously described in relation to the multicomponent fiber. Preferably, the ratio is such that the change in the porosity of the filtration media through degradation of the second fiber component is not sufficient to hinder the filtration performance of the resultant microfilament filter. In a particular embodiment, the microfilament filter prepared according to the method described herein exhibits a filtration performance such that greater than or equal to about 99% of particles having a diameter of 1 micron or greater are retained by the microfilament filter.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teaching presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

1. A splittable, multicomponent fiber having an outer surface, said fiber comprising: a first fiber component comprising a polymer having a melting point of at least about 200° C. and that does not degrade in a corrosive environment, said first fiber component being dimensioned to form a microfilament; and a second fiber component comprising a polymer having a melting point of at least about 200° C. and that is degradable in a corrosive environment; wherein each of said fiber components forms a portion of the outer surface of said fiber and form distinct, unocclusive cross-sectional segments along the length of the fiber.
 2. The multicomponent fiber according to claim 1, wherein said first fiber component comprises a polymer selected from the group consisting of polyphenylene sulfide, fluoropolymers, chlorofluoropolymers, epoxies, silicones, polymethylpentene, mixtures thereof, copolymers thereof, and terpolymers thereof.
 3. The multicomponent fiber according to claim 1, wherein said second fiber component comprises a polymer selected from the group consisting of polyesters and polyamides.
 4. The multicomponent fiber according to claim 3, wherein said second fiber component comprises a polymer selected from the group consisting of polycyclohexylene dimethyl terephthalate, polyethylene terephthalate, polybutylene terephthalate, poly(trimethylene) terephthalate, polyethylene naphthalate, nylon 6, nylon 6,6, mixtures thereof, copolymers thereof, and terpolymers thereof.
 5. The multicomponent fiber according to claim 1, wherein said first fiber component comprises polyphenylene sulfide and said second fiber component comprises polyethylene terephthalate.
 6. The multicomponent fiber according to claim 1, wherein said fiber is selected from the group consisting of pie/wedge fibers, hollow pie/wedge fibers, segmented round fibers, segmented oval fibers, segmented rectangular fibers, segmented cross fibers, and segmented multilobal fibers.
 7. The multicomponent fiber according to claim 1, wherein said fiber is selected from the group consisting of continuous filaments, staple fibers, spunbond fibers, and meltblown fibers.
 8. The multicomponent fiber according to claim 1, wherein said first fiber component comprises at least about 50% by weight of said multicomponent fiber.
 9. The multicomponent fiber according to claim 1, wherein said first fiber component comprises at least about 75% by weight of said multicomponent fiber.
 10. The multicomponent fiber according to claim 1, wherein said fiber is capable of being mechanically dissociated.
 11. The multicomponent fiber according to claim 10, wherein said mechanical dissociation comprises a method selected from the group consisting of carding, crimping, drawing, and high pressure water jet impinging.
 12. The multicomponent fiber according to claim 1, wherein said fiber is capable of being chemically dissociated.
 13. A fabric comprising a multicomponent fiber according to claim
 1. 14. The fabric of claim 13, wherein the fabric is selected from the group consisting of nonwoven fabrics, woven fabrics, and knit fabrics.
 15. A filtration media comprising a multicomponent fiber according to claim
 1. 16. The filtration media according to claim 15, wherein said filtration media further comprises one or more non-splittable fiber comprising a polymer having a melting point of at least about 200° C. and that does not degrade in a corrosive environment
 17. A method for preparing a microfilament filter at a point of use, said method comprising: a. providing a filtration media comprising a splittable, multicomponent fiber having an outer surface, said fiber comprising: i. a first fiber component comprising a polymer having a melting point of at least about 200° C. and that does not degrade in a corrosive environment; and ii. a second fiber component comprising a polymer having a melting point of at least about 200° C. and that does degrade in a corrosive environment; wherein each of said fiber components forms a portion of the outer surface of said fiber and form distinct, unocclusive cross-sectional segments along the length of the fiber; b. installing said filtration media at said point of use; and c. flowing a stream for filtration through said filtration media under high temperature, corrosive conditions such that said second fiber component degrades and said first fiber component remains intact as microfilaments having a fineness of less than or equal to about 1 denier per filament.
 18. The method according to claim 17, wherein said filtration media further comprises one or more non-splittable fibers comprising a polymer having a melting point of at least about 200° C. and that does not degrade in a corrosive environment.
 19. The method according to claim 17, wherein said microfilament filter prepared according to said method has a filtration performance of greater than or equal to about 99%, said filtration performance being measured as the percentage of particles having a diameter of 1 micron or greater that are retained by said microfilament filter.
 20. The method according to claim 17, further comprising removing said degraded second fiber component from said microfilament filter.
 21. The method according to claim 20, wherein said removing step comprises entraining the degraded second fiber component in the filtered stream exiting the filtration media such that the degraded second fiber component is carried away by said filtered stream.
 22. The method according to claim 20, wherein said removing step comprises mechanical cleaning of said microfilament filter.
 23. The method according to claim 17, wherein said stream comprises a gas.
 24. The method according to claim 17, wherein said multicomponent fiber is selected from the group consisting of continuous filaments, staple fibers, spunbond fibers, and meltblown fibers.
 25. The method according to claim 17, wherein said filtration media comprises a fabric selected from the group consisting of nonwoven fabrics, woven fabrics, and knit fabrics.
 26. The method according to claim 17, wherein said point of use comprises a baghouse filter.
 27. A microfilament filter prepared according to the method of claim
 17. 28. A filter comprising polyphenylene sulfide microfilaments having a fineness of less than or equal to about 1 denier per filament, wherein said filter has a filtration performance of greater than or equal to about 95%, said filtration performance being measured as the percentage of particles having a diameter of 1 micron or greater that are retained by said filter.
 29. The filter according to claim 28, wherein said filter has a filtration performance of greater than or equal to about 99%. 